1. Technical Field of the Invention
This invention relates to a prosthetic device for a human being. The invention further relates to an artificial ankle joint, referred to herein as an artificial ankle. The invention still further relates to an artificial ankle which operates to enable an artificial foot to move in multiple axial directions.
2. Description of the Prior Art and Problems Solved
It is known that a person who loses a foot and an ankle can employ a prosthetic device to replace the lost foot and ankle to thereby enable the person to stand in an erect position and to walk without extrinsic assistance, such as by use of a cane or a crutch.
It is known that a natural ankle receives the weight of the body transmitted to it by the bones of the lower leg, i.e., the tibia and the fibula, and then distributes the weight to the sole of the foot and ultimately to ground. A problem encountered in the use of an artificial ankle and foot involves the capability of the combination to dampen and/or to absorb shock caused by forces generated by the weight of the body and then to distribute the weight to ground.
It is known that a natural ankle enables a foot to move to a toe down-heel up position, and to a toe up-heel down position. In geometric terms, the toe down position increases the angle between the front of the foot and the leg, and the toe up position decreases the angle between the front of the foot and the leg. These movements in a natural ankle are produced by rotation of the foot in a first vertical plane around a first horizontal axis which passes through the ankle and which is perpendicular to the first vertical plane. The first vertical plane, in anatomical terminology, is called a sagittal plane and is sometimes referred to as a para sagittal plane. A specific sagittal plane, called the mid-sagittal plane, or the median plane, divides the body into right and left halves. Accordingly, for purposes of this disclosure, the sagittal plane which passes through the ankle is parallel to the median plane and divides the foot into right and left halves. The toe down-heel up position is referred to as plantar flexion, and the toe up-heel down position is referred to as dorsiflexion. The bottom of the foot, the sole, is referred to as the plantar, and the top of the foot is referred to as the dorsum or dorsal. Accordingly, another problem encountered in the use of the combination of an artificial ankle and an artificial foot is the capability of the artificial foot to produce plantar flexion and dorsifiexion.
It is known that a natural ankle enables a foot to move in left and right directions. Such movement in a natural ankle is produced by rotation of the foot in a second vertical plane around a second horizontal axis which passes through the ankle and which is perpendicular to the second vertical plane. The second vertical plane, in anatomical terminology, is called a frontal or a coronal plane. A coronal plane of interest herein divides the foot into a front portion, the toe end, and a rear portion, the heel end. The anatomical terms for the left and right movements depend upon the direction of the movement of the foot with regard to the previously mentioned median plane. Movement of the sole of the foot, the plantar, away from the median plane is called eversion, and movement of the sole of the foot, the plantar, towards the median plane is called inversion. Accordingly, still another problem encountered in the use of the combination of an artificial ankle and an artificial foot is the capability of the artificial foot to produce eversion and inversion.
The above mentioned first and second vertical planes are perpendicular each to the other. The intersection of the first and second vertical planes is a vertical line which passes through the ankle, and is, therefor, the line of action through which the weight of the body passes from the tibia and the fibula to the foot and ultimately to ground.
In addition to the intersecting first and second vertical planes, a horizontal plane, referred to as a transverse plane or an axial plane, also passes through the ankle and is perpendicular to each of the first and second vertical planes. The line of intersection of the first vertical plane and the horizontal plane is the above mentioned second horizontal axis. The second horizontal axis accordingly lies in the horizontal plane and the first vertical plane. The line of intersection of the second vertical plane and the horizontal plane is the above mentioned first horizontal axis. The first horizontal axis accordingly lies in the horizontal plane an the second vertical plane. The first and second horizontal axes are perpendicular each to the other and intersect at a point in the center of the ankle.
There is a need for an artificial foot having an artificial ankle with sufficient flexibility to permit distribution of vertically applied weight of the body, and to enable the artificial foot to produce plantar flexion, dorsiflexion, eversion and inversion.